Pulverizing process and apparatus



Jan. 16, 1934. a PEDELTY Re. 19,049

PULVERIZING PROCESS AND APPARATUS Original Filed Feb. 27, 1929' INVENTOR.

W M PM? ATTORNEY}:

R ina Jan; 1 1934 runvmuzma raocsss armas'rus 'wauer B. Pedelty, Masoncm, Iowa Original No. 1,783,975, dated December 9,1930,

Serial No. 343.078, February 27, 1929. 'Applicagisolnnfzor rei'llue July18,1981. Serial No.

This invention relates to improvements in pulverizing procexes andapparatus of the general type employed for feeding finely divided fueltofurnaces.

In apparatus of this general type it is common to mount upon a singleshaft a set of breakers or grinders and a centrifugal fan for deliveringthe finely divided portions of material into the furnace. In the use ofsuch apparatus for feeding blast furnaces great diflicuities have beenexperienced by reason of the larger particles falling to the bottom ofthe retort while only partially consumed and becoming mixed with moltenmetal to form a slag which is very diiiicult to remove, blastingoperations being sometimes resorted for that purpose. I

To overcome this difficulty various expedients have been tried, one ofthe most common being to provide a wall or shoulder between the breakingor grinding portion of the apparatus and the fan in order to obstructthe passage of the larger fragments into the fan while allowing thesmaller fragments to be thrown 'over such wall or shoulder. Thisexpedient has proven effective to a considerable extent in keeping thelarger fragments out of the fan but it has not prevented slag formingfragments from passing through the fan to the furnace.

The primary object of my invention is to reduce pulverizable materialsby entraining such materials in an elastic fluid and churning orimpacting them against each other in afield or maelstrom of eddiesinduced by the operation of a centrifugal fan at one side of said field,the mateerials or fragments of materials being caused to impinge uponeach other throughout the field while moving freely and promiscuously invarious directions.

My invention is distinguished from a pulverizing apparatus in whichmaterials and air are mechanically propelled and driven into contactwith each other in such a manner as to produce crushing and abradingcontacts, and which propelling operation requires to be many timesrepeated in order to reduce solid materials to the condition of apowderor a dust. In the practice of my process, the material ispreferably, drawn into the pulverizing field by suction and after it hasonce entered such field it is held in suspense without contact withmoving mechanical driving mechanism until reduced to the desired degreeof fineness determined by the carrying capacity of I an outflowingorcentrifugally discharging stream. in contact with each other in thedescribed manof air. ner.

More particularly stated it-is an object of my My process alsocontemplates a continuous deinvention to provide a fan which willeffectively agitate small fragments of fuel and similar material ormaterials capable of being entrained in air and pulverized by impact ofone portion upon another within a fan, casing and atone side of the fanwings as to cause them to break or pulvverize each other so completelythat the material may be delivered from the fan casing substantially inthe form of dust andwhereby solid substantially capable of suspension inthe heated atmosphere of the furnace or retort untilfully consumed. i

My invention rests upon the discovery that a fan may be so constructedthat the major portion of the material will not reach the space occupiedby the wings until after it has been caught in one or more powerfuleddies or conflicting aircurrents and thrown violently against otherparticles of the material with impacting and grinding effects,whereby'the material is almost instantaneously reduced to a size havingthe char,-

held in suspension in the atmosphere for a considerable period of time.

of this invention to provide a process for utilizing violently agitatingair to efiect a final vpulverization of material and to deliver suchmaterial in an air stream wherein it is capableof floating untilconsumed in a combustion chamber.

In the drawing:

Figure l is a side elevation of a pulverizing apparatus embodying myinvention. v

'Figure 2 is a sectional view of the fan as taken on line 22 of Figure1.

Figure 3 is a detail side view of the fan.

Like parts are identified by the same reference characters throughoutthe severalviews.

In the practice of my process I first reduce the material to smallfragments by any suitable means, these fragments being preferably ofsuch fineness that they can be entrained and carried in high velocityair streams. Thereupon I feed these fragments into a maelstrom of:violently agitating air having a multitude of gyrating or crosscurrents of such intensity as to entrain the particles of material andthrow them violently against each other and against any obstruction intheir path. The velocity and force of the air currents is proportionedto the force required for crushing the particles of material whenbrought fuels such as coal may be so pulverized as to be acteristic ofdust in that it is capable of being It may therefore be stated: that itis an object so livery of dust laden air from one side of the agitatingfield in which the fragments are being crushed and a correspondingcontinuous delivery of fragments to be reduced into said field fromanother side.

My preferred means for practicing the process and for feeding thematerial into and out of the space within which the material is beingreduced, will now be described more particularly with reference to theaccompanying drawing. 1 In the drawing, a breaker 10 of ordinaryconstruction is conventionally illustrated, from which fuel or othermaterial may be delivered through a chute or passage 11 to an inletopening 12 of a centrifugal fan casing 13. The breaker and the passage11 may be of any ordinary construction, or any desired means may besubstituted for initially reducing the material into comparative- 1ysmall fragments such as have heretofore been delivered to furnaces.

The casing 13 is similar in form to the casings of centrifugal fans incommon use, the inlet 12 being located at the so called eye or in theside wall of the casing opposite that at which the shaft 14 enters andthe outlet passage or chute 15 being tangential in order that the fanwings may throw air and other material in the desired direction.

I have discovered that by mounting upon the shaft 14 a set of fan wings17, preferably two wings diametrically opposite and of a widthapproximately one half to nearly two thirds that of the casing, it ispossible to set up gyrating currents and cross currents in the portionof the casing between the wings and the inlet side, and thereby throwthe fragments of material violently against each other and against theperipheral wall portion 18 of the casing in such a manner as to almostinstantly reduce. said fragments to dust.

If the fragments enter the spaces between the wings I! to y considerableextent I am unable to find any evidence of that fact. The wing surfacesdo not become polished and the encircling peripheral portion of thecasing does not become polished, even after prolonged periods of use. Itis evident that if any fragments enter the space between the wings theyare immediately thrown laterally and caught in the swirls and crosscurrents at the side of the wings. Air and finely divided particles are,however, constantly delivered through the outlet chute 15 in which nofragments of sufllcient size to be classed as other than dust have asyet been discovered, although repeated tests have been made of thematerial passing through this chute.

While eddies and cross currents of great intensity are developed in theunobstructed space between the inlet and the fan, there is little speedof general revolution about the axialline of the fan shaft projectedinto such space, for the reason that the direct action of the revolvingfan is outside of this space, and the eddies tend to break up therevolving air currents which would otherwise be generated by friction ofthe air which is being carried around by the fan wings in the spaceoccupied by the fan. Therefore, but little centrifugal force isdeveloped as compared with that developed in the peripheral spaceencircling the fanwings, and the tangentially outiiowing air can entrainand carry with it only those particles which have been completelyreduced to a substantially impalpable powder or dust.

The rapidity with which fragments of coal or similar material may bereduced to a dust indicates that the vortex or maelstrom developed inthe open space between the inlet and the fan wings is composed largelyof a multitude of eddies each revolving about its own axis, whereas, allof these eddies also travel in a circular path about the central axis ofthe fan shaft extended. Also, there appears to be a pulsating movementdue to the fact that, as the fan revolves, the air in the space which itoccupies tends to become compressed in front of the wings and a vacuumtends to develop in the rear of the wings with the result that the airin front of the wings is not only driven" outwardly by centrifugalforce, but develops a strong tendency to flow laterally into the spacebetween the fan and that wall of the casing which is provided with theinlet, whereas, air and other material in such space tends to develop acounter-flow toward the rear side of each wing. The air and othermaterial entering through the inlet, is also necessarily flowing in ageneral direction perpendicular to the plane of the vortex, and thecombined effect is to increase the random element to a point wherecollisions take place with almost inconceivable frequency.

It also appears probable that the multitude of cross currents, developedby the pulsating effects of the fan wings and by the incoming material,operate to so diminish the general movement of revolution about thecentral axis as-to prevent centrifugal force from developing in thevortex space to a degree suflicient to carry the larger fragments out ofthe vortex zone, and this appears to account for the fact that only dustladen air passes through the outlet chute.

In my improved fan I employ wings 1'1 having flat convergent surfaces,the wings being therefore wedge shaped, with the tips or outer marginssubstantially parallel to the, shaft axis. Fan wings of this generaltype are disclosed in my former patent for a centrifugal fan datedSeptember 27, 192'? and numbered 1,463,317 but for the purpose of mypresent invention I prefer to construct these wings of cast steel,suitably cored to reduce their weight. I

Apparently the form of the wings and the fact that but two diametricallyopposite wings are employed, are material factors in developing thenecessary agitation in the air between the inlet and the wings. Howeverthis may be, as compared with results obtainable from some of the othertypes of fans, it is certain that in a large part the results abovedescribed are obtained by reducing the width of the wings so as to allowa considerable space between them and the inlet side of the fan casing.I have found that with wings constructed as above described I obtain thebest results by mounting the wings on the shaft in close proximity tothe closed wall of the casing and provide space between them and theinlet side of the casing, of a width more than half that of the wings.

Such a fan delivers the fuel dust in a pulsating v current of highfrequency, and these pulsations are also an effective aid to combustionin that they tend to break up circulation streams of the gases in thecombustion chamber.

By employing a two wing fan having a diameter of about twenty two inchesfrom the tip of one wing to the tip of the other with blades about eightinches in width, a casing inlet about sixteen inches in diameter, and anoutlet about twelve inches square, with approximately four and one-halfinches between the inlet side of the casing and the fan wings, and byrevolving sucha fan at approximately 2000 R. P. M., I am enabled tocompletely reduce the coal fragments to a dust and to deliver such dustto a burner in a pulsating current as above described, without causingthe fan wings to become abraded or even polished and with only a lightpolishing effect upon that portion of the casing which encircles thefour and one-half inch space at one side of the fan wings.

I claim:

1. The process of pulverizing and feeding fuel consisting in generatinga vortex in unobstructed space, feeding air and entrained fragments offuel into such vortex at one side thereof, and subjecting the vortex atthe opposite side to pulsating agitation tending to develop crosscurrents and counter-currents.

2. The process of pulverizing material, consisting in generating arevolving, churning maelstrom of such material and an elastic fluidwithin an unobstructed whorl shaped space which includes the, axis ofthe whorl, feeding elastic fluid and material to be pulverized into saidmaelstrom at' one side thereof, and maintaining the entrained materialin suspension in the elastic fluid with the particles in shearingrelation to each other, and otherwise unsupported and unobstructed as todirection of motion and delivering the pulverized material from saidmaelstrom tangentially when the particles are sufliciently reduced insize to be carried with portions of the elastic fluid out of saidmaelstrom by centrifugal force.

3. The process of treating material which consists in generating avortex, continuously feeding vortex maintaining material into saidvortex at one side thereof and along its central axis, and

subjecting the vortex at the opposite side to rota tive pressure, andcontinuously releasing material from the peripheral portions of thevortex, the space occupied by said vortex being unobstructed from itsaxis radially to its peripheral portions.

4. A method of impelling a fluid body laden with pulverulent material,consisting in the development of a vorticose movement of said fluid bodywithin an otherwise unoccupied enclosed space, continuously releasingmaterial laden fluid tangentially from said space and feeding materialladen fluid to the central portion of said space, and maintaining saidvorticose movement by rotative agitation of fluid at the side of saidspace opposite the infeeding side.

5. The combination with a casing of the centrifugal fan type providedwith a tangential outlet and an inlet in one side wall, said casinghaving an interior open and unobstructed receiving space extending fromthe inlet to the central portion of the casing in free communicationwith the tangential outlet, a shaft extending through the wall of thecasing opposite the inlet, and paddle-shaped wings secured to said shaftfor revolution at one side of said receiving space and adapted todevelop a vorticose movement of air and entrained material in saidreceiving space while substantially excluding such material from betweenthe wings, whereby the air and entrained material may be propelledthrough the tangential outlet under the centrifugal force developed inthe receiving space, said wings having relatively thick central portionsof substantially the same width as the outer portions.

WALTER B. PEDELTY.

